Combination one-and two-digit selector switches



Nov. 20, 1951 H. w. BALZER COMBINATION ONE AND TWO DIGIT SELECTOR SWITCHES Filed Oct. 27, 1947 INVENTOR. HARVEY W. BALZER MmJmmIN H OOOO H O an 0 o E 333 56 w 5.2 25 5 of .G 96 m N28 3:? o D o O 0 M M mm m u 1 Q2 .55 E8 ATTORN EY Patented Nov. 20, 1951 COMBINATION ONE- AND TWO-DIGIT SELECTOR SWITCHES Harvey W. Balzer, Downers Grove, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application October 27, 1947, Serial No. 782,420

8 Claims.

This invention relates in general to automatic telephone systems, and more particularly to selector switches employed in such systems for selecting trunk paths to other switches or circuits in the train.

It is an object of the invention to provide an improved selector switch operable either by means of a single digit for selecting a free trunk of one group of trunks or by means of two digits for selecting a free trunk in another group of trunks.

Another object of the invention is to provide new and novel means for causing a selector switch to stop on the last trunk of a group of trunks, for returning busy tone to the calling station when said last trunk is in prior use, and for causing the selector switch to seize said last trunk when the last trunk is in the idle position.

A feature of the invention resides in the novel arrangement wherein a relay is caused to partially operate when the last trunk of a. group is reached for the purpose of stopping the selector switch on the last trunk regardless of whether the last trunk is found in a busy position or an idle position, the said relay operating fully should the last trunk be found in the busy position for the purpose of'causing busy tone to be connected to the selector switch, and a second relay operating simultaneously with said first relay should the last trunk be found in the idle position for the purpose of disabling said first relay before said first relay has had time to operate fully and cause busy tone to be connected to the selector switch.

There are other objects and features of the invention having to do for the most part with the details in carrying out the foregoing. The various objects and features of the invention will be understood best upon a further perusal of the specification, reference being had to the accompanying drawing which shows by means of a conventional circuit diagram a sufiicient amount of apparatus to enable the invention to be described and understood.

The selector switch shown in the drawing comprises the well-known Strowger switch mechanism of the 400-point type having vertical and rotary movement. Associated with this Strowjger mechanism is a switch spring set I16, known as a normal post spring set. This spring set operates when the switch shaft is raised to a predetermined bank level, or levels, responsive to the dialing of the first digit for the purpose of tion. The Strowger mechanism further includes a set of switching springs I26 which are actu ated by the movement of the switch shaft in the vertical direction away from its normal position, and a set of switching springs Ill and H8 which are actuated by the movement of the switch shaft into its eleventh rotary position. The selector switch also includes a line relay I20, 2. hold relay I30, a stepping relay I80, a trunk group stopping relay 160, a switching through relay I I0 and other control relays.

The selector switch has access, by way of its wipers, to ten bank levels any one of which is selected by the dialing of the related digit. Bank levels not associated with the operation of normal post spring set I16 have automatic rotation, i. e., an idle trunk in such a bank level is automatically selected followingthe pulsing of the switch shaft to the bank level. Bank levels directly associated with the operation of normal post spring set I16 do not have automatic rotation for selecting a particular group of trunks, as the operation of normal post spring set H6 changes the control of the rotary movement from automatic stepping to dial controlled stepping for the selection of a trunk group.

The EC bank contacts of one digit levels have no function. The C bank contacts of one digit levels are normally connected to battery potential when the related trunks are in idle positions, and to ground potential when the related trunk are in busy positions. The EC bank contacts of two digit levels are divided into one or more trunk groups, the last EC' contact of each such trunk group being permanently connected to ground potential. In the accompanying drawing, the first three EC' contacts constitute one trunk group, the next five 120' contacts constitute another trunk group, the last two EC' contacts of the level not being shown. The 0' bank contacts of two digit levels are normally connected to battery potential when the related trunks are in idle positions, and to ground potential when the related trunks are in busy positions.

It should be undertsood at this time that while the embodiment of the present invention disclosed and described in this specification includes the well-known Strowger selector switch of definite bank capacity, the invention is not limited to the particular form shown but may utilize other bank capacities or type of switch. It should be further understood that while a plurality of battery connections are shown in the drawing, they are preferably the-same battery. Also, in

Whenever the selector shown in the drawing is in the idle, or free, position; battery through the upper winding of relay I will be found on the C conductor I25. A preceding .switch'or circuit seizing this selector connects ground to conductor I24 thereby causing relay I10 to operate. At the same time a metallic loop iscompleted across conductors I22 and I23 thus causing relay I to operate. The'operation of relay I10 prepares a number of circuits, and the operation of relay I20 causes relay I to operate from ground, armature H0, armature I2I and working contact, winding of relay I30 to battery.

' At armature I33, relay I30 "connects ground potential to conductor I24 for the purpose of guarding the'connection against intrusion; and, at armature I34, causes relay I to operate from ground, armatures I33, I34, armature Ill and working'contact, armature I45 and resting contact, winding of relay I to battery. At armature I6 I, relay IEO transfers the lower winding of relay I20 from'direct ground to dial tone and ground to inform the calling person-that dialing. of this selector may now commence.

The calling person then dials the wanted level of the selector, and the loop circuit to relay I25 is accordingly interrupted the number of times corresponding to the digit dialed. With each restoration of relay I20, the circuit to relay I30 is opened at the working contact of armature IZI but relay ,I30 is of the slow-to-release type and, therefore, remains operated during the pulsing; and a circuit is completed in' multiple to the lower winding of relay I10 and vertical magnet IE5 at armature I2I 'and resting contact. Vertical mag net I55 accordingly raises the switch shaft and wipers I30, I31, I38 and I39 to the dialed level in the well-known Strowger manner, the vertical off-normal spring set I26 operating with the first vertical step. At armature spring I29, V. O. N. spring set I25 opens the circuit of the upper winding of relay I10; and, at armature spring I21, V. O.N. spring set I26 causes relay I to operate from ground, armature I33, armature spring I21, armature II5 and'resting contact, armature I32, armature I55 and resting contact, armature I44, cam spring set II8, interrupter armature I14, winding of relay I80 to battery. At armature I8I, relay I80 shunts out cam spring set II8.

Upon the completion of :the pulsing, relay I20 comes to rest in the operated position thereby maintaining the circuit to relay I30 at armature I2! and working contact. Relay I30, therefore, cannot restore at this time. Relay I10, however, restores shortly thereafter because the circuit to its upperwinding is open at spring I29 of V. O. N. spring set I25, and the circuit to its lower winding is now open at the resting contact of armature I2I. .At the working contact of armature I1I, relay I10 opens the circuit to relay I50, causing'relay I50 to restore; and. at armature I12, further opens the multiple circuit toits lower winding andvertical magnet I55. At armature I 54, relay I50 causes rotary magnet H5 to operate from ground, varmatures I64, I41, I82, winding of rotary magnet I15 to battery; and, at armature {6 1, replaces the dial tone.- and ground on the lower winding of relay I20 with direct ground. Rotary magnet I15 accordingly rotates the shaft and wipers one step in the bank level selected by the vertical pulsing. The operation of rotary magnet I15 also opens the circuit to relay I80 at interrupter armature I15, causing relay J80 to'restore and open the circuit to rotary'magnet I15 at armature I82; The operation of the selector at this moment is dependent upon Whether the trunk connected to the first bank contact set selected by the vertical pulsing is in prior use or isfree.

\ Should the trunk connected to the first bank contact set be free, then wiper I38 of the selector encounters "battery supplied from the selected trunk to the"C'contact of the first bank contact set, and a circuit for the upper winding of relay I I3 is completed from ground, armature I43, ISI, upper winding of relay H3, wiper I38 to battery on the C contact connected to wiper I38, causing relay I I0 to operate before rotary magnet I15 can restore and complete the circuit to relay I80 at interrupter armature il l. 'Relay I-III closes its,X contacts I I5firsttherebycompleting the circuit to its lower winding which causes relay .0 to operate fully. At the resting contactof armature H5, relay H0 opens a further point in the circuit to relay I80 t'oprevent any further possible rotation across the selected bank level: at armature II3, extends ground potential to C wiper E38 thereby shunting its upper winding: at armatures III and H2, opens the loop circuit of .relay I20, causing relay to restore: at armatures III and H2 and respective working contacts, extends conductors I22 and I23 through to wipers I35 and I31; and, at armature I I5, opens the circuit of relay I30, relay I30 restoring after a short interval. R0- tary magnet I15 restores and partl prepares a circuit to relay I80 but the circuit is still open at the resting contact of armature I I5.

The restoration of relay I20 opens a point in the circuit to relay I I30, and also partly prepares the circuit to release magnet E25. At armature I33, relay I30 removes ground potential from C conductor I25 thereby opening the circuit of the lower winding of relay H5 .and removing the ground shunt from the upper winding of relay I'I0. .Relay H0 is now held operated-over the circuit from ground on the C bank contact connected to wiper I 38 (ground potential being connected to the C bank contact as one-result of the switching through of conductors I22 and I23 to the selected trunk ahead), wiper 538, armature II3, spring 121 of V. O. N. spring set i26, armature I I5 and working contact, lower Winding of relay IIO to-batter-y.- The ground from wiper I38 through armature I I3 is also thereby extended to C conductor I2 3 to retain the circuit preceding this selector and also to guard the connection-from intrusion.

Should the trunkconnected to the first bank contact set be in prior use, then wiper I38 of. the selector encounters ground potential on the C contact of the first bank contact set and, consequently, relay I-I0 cannot operate at, this time. The circuit to relay I80 is, therefore, completed at interrupter armature I14 when rotary magnet I15- restores, causing relay i853 to re-operate and again completethe circuit to rotary magnet I15 at'armature I82. Rotary'magnet I15 re-operat-es, advances the selector switch shaft and wipers a second rotary-;st ep, an d again opens the circuit to relay I80 Thisinteraction; between;roteu y ma n I15v an .lt-el .ceninu a n wine? ing this selector.

I38 encounters battery potential on the C contact of a bank contact set connected to a free trunk or until wipers I36, I31, I38 and I39 are advanced to the eleventh position of the banks. In the latter event cam spring sets H1 and H8 are operated, busy tone and ground is connected to the lower winding of relay I20 in place of direct ground, and a further point in the circuit of relay I80 is opened at cam spring set II8. Rotary magnet I restores but relay I80 cannot again re-operate.

Assuming now that the selector has selected a free trunk, then relay I I0 is operated in the manner previously explained, and the calling person's transmission circuit is extended through to the selected trunk. From this point on, the connection may be extended to other switches or circuits in any well-known manner according to need or desire, but since such arrangements are not part of the present invention, it is deemed unnecessary to include further details in this specification. Upon the completion of the conversation the caling person disconnects, whereupon ground potential is removed from the C contact connected to wiper I38 in any well-known manner, causing relay IIO of the selector to restore. At armatures III and H2, relay IIO switches conductors I22 and I23 from wipers I35 and I31 to relay I: at armature II3, disconnects C conductor I24 from wiper I 33; and, at armature I I6, completes the circuit to release magnet I25. The operation of release magnet I25 causes the selector to be restored to normal in the well-known Strowger manner,,and the circuit of release magnet I25 is opened at spring I28 of V. O. N. spring set I20 as the selector switch shaft reaches its normal position.

Should the calling person fail to obtain a free trunk, then busy tone and ground is connected to the lower Winding of relay I20, as previously explained. Upon hearing the busy tone, the calling person disconnects thereby opening the loop circuit to relay I20. Relay I20 restores and, at armature I2I, opens the circuit to relay I30 and partly prepares the circuit to release magnet I25. Relay I30 restores after a short interval and, at armature I and resting contact completes the circuit to release magnet I25. At armature I33, relay I30 removes ground potential from C conductor I24 thereby to free the circuit precednet I25 causes the selector to be restored to normal in the well-known Strowger manner, and the circuit of release magnet I25 is opened at spring I28 of V. O. N. spring set I26 as the selector switch shaft reaches its normal position.

Two digit operation The seizure and vertical stepping operations of the selector for two digit service are essentially the same as described in the preceding section for one digit service plus the added operation that, as the selector switch shaft and wipers are raised to a two digit bank level, normal post spring set I16 is operated.

The operation on N. P. spring set I16 completes a multiple circuit for operated relay I60 from ground, armature I33, spring I21 of V. O. N. spring Set I26, armature H5 and resting contact, armatures I32, I54, N. P. spring set I16, armature I and resting contact, winding of relay I to battery. The operation of N. P. spring set I16 also partly prepares a circuit for relay I40. v

Shortly after the completion of the, vertical stepping;- relay I10 restores to normalfor the The operation of release magwipers I36, I31,

reasons given in the preceding section concerning one digit operation. At armature I1I, relay I10 opens one of the multiple circuits to relay I: at armature I12, further opens the multiple circuit to its lower winding and vertical magnet I; and, at armature HI and resting contact, causes relay I40 to operate from ground, armature I33, spring I21 of V. O. N. spring set I26, armature I I5 and resting contact, armatures I32, I54, N. P. spring set I16, armature HI and resting contact, winding of relay I40 to battery. Relay I40 locks to the circuit from ground, armature I33, spring I21 of V. O. N. spring set I26, armature H5 and resting contact, armatures I32, I54, N. P. spring set I 16, armature I45 and working contact, winding of relay I 30 to battery.

At armature I45, relay I40 opens the second multiple circuit to relay I60, causing relay I60 to restore: at armature I43, opens the circuit to relay I80, causing relay I to restore; and, at armature I46, causes relay I10 to re-operate from ground, armatures I33, I46, I56, upper winding of relay I10 to battery. At armature I8I, relay I80 removes the shunt from cam spring set H8; and, at armature I82, opens a further point in the circuit of rotary magnet I15. At the resting contact of armature I6I, relay I60 replaces dial tone and ground on the lower winding of relay I20 with direct ground; and, at armature I64, partly prepares a circuit to rotary magnet I 15. At armature I1I andworking contact, relay I10 connects a multiple ground to the winding of relay I40 by way of armature I33, I34, and armature I35 and working contact.

The calling person then dials the second, or rotary stepping, digit of the selector, and the loop circuit to relay I20 is accordingly interrupted the number of times corresponding to the digit just dialed. With each restoration of relay I 20, the circuit to relay I 30 is opened at the working contact of armature I2I but relay I30 is of the slowto-release type and, therefore, remains operated during the pulsing; and a circuit is completed in multiple to the lower winding of relay I10 and rotary magnet I15 at armature I2I and resting contact. This multiple circuit may be traced from ground, armature II S, armature I2I and resting contact, armature I35 and Working contact, armature I12, lower winding of relay I10 to battery and through armature I12, armature I48 and Working contact, armature I13, winding of rotary magnet I15 to battery. Rotary magnet I1 5 accordingly operates and restores for each dialed pulse and rotates the selector shaft and I38 and I30 across the bank level selected by the vertical pulsing to the dialed bank contact set in the well-known Strowger manner.

With the first restoration of relay I20 responsive to the dialing of the second digit, a circuit is completed for relay I50 from ground, armature II'o, armature I2! and resting contact, armature I35 and Working contact, armature I12, armature I48 and working contact, armature I58, upper winding of relay I50 to battery, causing relay I50 to operate its X contact (at armature I59) thereby to fully operate and lock relay I50 to the circuit from ground, armatures I33, I59, lower winding of relay I50 to battery. At armature I 58, relay I50 opens the circuit to its upper Winding: at armature I51 partly prepares a multiple circuit to rotary magnet I15: at armature I56, opens the circuit to the upper winding of relay I10, and at armature I54, opens one of the multiple cir? cuits to relay I40;

Upon the. .completionof the pulsing of the second-digiturelay I20 comes to rest in the operated position thereby maintaining the circuit to relay I'M-:61 armature I2I and working contact. Relay -l'30, therefore, cannot restore at this time. Belay I18, however, restores shortly thereafter because the circuits to its upper winding are open at spring I29 of V. O. N. spring set I28 and at armature I56, and the circuit to its lower winding is now open at the resting contact of armature 'I2I. At armature I'II, relay I10 disconnect the remaining ground from the winding of relay I46, causing relay I40 to restore. At armature I42, relay I40 connects the winding of relay I60 to the EC. wiper I39: at armature I43, connects ground potential to the upper winding of relay IIB: at armature I41, partly prepares a circuit to rotary magnet I; and, at armature I 44, causes relay I88 to operate from ground, armature I33, spring 121 of V. O. N. spring set I26, armature I I5 and resting contact, armature I32, armature I55 and working contact, armature I63 and resting contact, armature I44, cam spring set IIB, interrupter armature I 14, winding of relay I88 to battery. At armature ISI, relay I80 shunts out cam spring set H8; and, at armature I82, causes rotary magnet to operate from multiple ground on armature I41, armature I82, winding of rotary magnet I15 to battery. Rotary magnet I15 accordingly steps the wipers I 36, I31, ISBand I 39 to the dialed bank contact set of the wanted group of trunks in the well-known StroWger manner. The operation of the selector at this moment is dependent upon whether the dialed trunk is in prior use or is free.

Should the dialed trunk be free, then C wiper I38 encounters battery supplied from the dialed trunk-to the C contact connected to wiper I38,

and a circuit for the upper winding of relay IIQ is-completed from ground, armature I43, I31, upperwinding of relay IIO, wiper I38 to battery on the C contact connected to wiper I38, causing relay I III to operate before rotary magnet I15 can-again restore and again complete the circuit to relay I80 at interrupter armature I14. Relay I I0 closes its X contact I I5 first thereby completingthe circuit to its lower winding which causes relay I I0 to operate fully. At the resting contact of armature II5, relay IIO opens a further point in the circuit to relay I80 to prevent any further possible rotation in the selected trunk group: at armature II3, extends ground potential to "C wiper I38 thereby shunting its upper winding: at armatures II I and H2, opens to'restore: at armatures III and II 2 and respective working contacts, extends conductors I22 and I23 to wipers I36 and I31; and at armature II6, opens the circuit to relay I30, relay I restoring after a short interval. Rotary magnet I 15 restores and partly prepares a circuit to relay I80 but the circuit is still open at the resting contact of armature H5.

"The restoration of relay I20.opens a point in the circuit to relay I30 and also partly prepares the circuit to release magnet I25. At armature I33, relay I30 removes ground from C conductor I24 thereby opening the circuit of the lower winding of relay H0 and removing the ground shunt'from the upper winding of relay IIO. Relay H0 and I are now held operated over the circuit from ground on the C' bank contact connected to wiper I38 (ground potential being connectedto' the C bankcontact as one result of the "switching through of conductors I22 and I23 to the selected trunk saheadiawiper I38, armature II3, spring I21 of V. spring set I26, armature H5 and working contact, lower winding of relay III] to battery and through armature II3,'armature I-59, lower-winding to: relay I50 to battery. The ground from wiper I38 through armature II 3 -is=-also thereby'iextended to C conductor I24 to retainthe-circuit preceding this selector and a1so-to guard the connection against intrusion.

Should the dialed trunk be in prior use and it is not the last trunk of the group, then wiper I38 of the selector encountersground potential on the C contact of the dialed trunk and, consequently, relay I I0 cannot operate at'this time. The circuit to relay I80 is, therefore, completed at interrupter armature I14 when rotary mag,- net I15 restores the last time as a result of the dialing of the second digit, causing relay--I80;to again'cperate and again complete-the circuit to rotary magnet I15 at armature I82. Rotary magnet I15 again operates, advances wipers1I36, I31, I38 and I39 to the bank contact set of the next trunk in the group, and again opens the circuit to relay I80. This interaction between rotary magnet I15 and relay I80'continues until wiper I38 encounters battery potential on the 0 contact of a free trunk of the group or until the last trunk of the group is reached.

Assuming further that the last trunk of the group has been reached in the manner'just described, and that the last trunk of the group is in prior use, then wiper I38 of the selector en counters ground potential on the 'C bank c0ntact of the last trunk, and relay" II 0, therefore, cannot operate. At the same time, E. C." wiper I39 encounters ground potential on the E. 0 bank contact of the last trunk,and relay I60 of the selector operates from this ground "potential by way of armatures I52, I42, II4, I62, winding of relay I60 to battery. Relay I60 operates its X contact (armature I63) first thereby :"completing a locking circuit from ground, armature I33, spring I21 of V. O. N. spring set I26, armature H5 and resting contact, armature I32, armature I and working contact, armature. I63 and working contact, winding ofrelay I to battery. At the resting contact of armature I63, relay I60 opens a point in the circuit to relay I88 before rotary magnet I15 can again restore and again complete the circuit to relay I at interrupter armature I14 thereby eliminating any possibility of the selector wipers, beingrotated from the bank contacts of the last'trunk of the group. At armature I62, relay I60 .disconnects E. C. wiper I39 from the winding of relay I60; and, at armature I62 and working contact, causes relay I40 to operate from ground, armature I 33, springl21 of V. O. N. spring set I26, armature H5 and resting contact, armature I32, armature I55 and working contact,.armature Hi3 and working contact, armature I62 and working contact, armature I53, windingof relay I40 to battery. Rotary magnet I15 restores for the last time and partly prepares a circuit to relay I80 butthe circuit is still open at the resting contact of armature I63. At armature I4I, relay I40 replaces direct ground on the lower winding of relay I20 with busy tone and ground to indicate to the calling person that all of the trunks of .the group are in prior use. -At armature I43, relay I40 disconnects ground potential fromthe upper winding of relay IIO toprevent relay 1 I I0 from later operating and switch-ing through should the occupied trunk become free before the calling person disconnects.

Should'the last trunk of the group be free when the selector switch wipers reach the last trunk, then wiper I33 encounters battery on the C bank contact and relay He immediately operates and locks in the manner previously described. At the same time, wiper its encounters ground potential on the E. C!" bank contact and relay Its operates its X contact (armature I63). Relay ltd, however, cannot operate fully or look because the simultaneous operation of relay IIB opens the locking circuit of relay I60 at armature H5 and the starting circuit of relay I69 at armature II4. Relay IIEJ, therefore, at this time performs the function of disabling relay ISO in addition to performing the operations detailed in the previous paragraph reading Should the dialed trunk be free Assuming now that the selector has selected a free trunk in the wanted group, then relay H8 is operated in the manner previously explained and the calling persons transmission circuit is extended through to the selected trunk. From this point on, the connection may be extended to other switches or circuits in any wellknown manner accordingto need oi-desire, but since such arrangements are not. part. of the present invention it is deemed unnecessary to include further details in this specification. Upon the completion of the conversation the calling person disconnects, whereupon ground potential is removed from the contact connected to wiper I38 in any well-known manner,

causing relays HE! and I50 to restore. At arma- 1 tures III and H2, relay Iii? switches conductors I22 and I23 from wipers I58 and I3? to relay I26: at armature II3, disconnects C conductor I24 from wiper I38; and, at armature IIE, completes the circuit to release magnet 25. The operation of release magnet I25 causes the selector to be restored to normal in the wellknown Strowger manner, and the circuit of release magnet I25 is opened at spring I28 of V. O. N. spring set I26 as the selector switch shaft reaches its normal position.

Should the calling person fail to obtain a free trunk in the desired group, then busy tone and ground is connected to the lower winding of relay I26, as previously explained. Upon hearing the busy tone, the calling person disconnects thereby opening the loop circuit to relay I29. Relay I29 restores and, at armature I25, opens the circuit to relay I36 and partly prepares the circuit to release magnet I25. stores after a short interval and, at armature IBii and resting contact, completes the circuit to release magnet I25. At armature I32, relay 39 opens the locking circuits of relays Edd and IE8, causing relays I40 and I66 to restore: at armature I33, opens the locking circuit of relay I58, causing relay Ii] to restore; and, at armature I33, relay I36 also removes ground potential from C conductor I24 thereby to free the circuit preceding this selector. The operation of release magnet I causes the switch shaft and wipers of the selector to be restored to normal position in the well-known Strowger manner. As the switch shaft drops from the dialed trunk bank level, N. P. spring set I16 returns to normal position, and the circuit of release magnet I25 is opened at spring I28 of V. O. N. spring setIZB as the switch shaft reaches its normal position.

What is claimed is:

1. In a telephone system, a group of switches,

Belay I33 re- ILA a group of trunks accessible to said switches, means for'causing any one of said switches to select the last trunk of said trunk group, a relay operated in response to the selection of said last trunk by one of said switches, means for locking said operated relay when said one switch selects said last trunk at a time said last trunk is in a busy position, and means responsive to the iocking of said operated relay for preventing further selective action of said one switch and for causing busy tone to be connected to said one switch.

2. The telephone system as claimed in claim 1 together with means for causing said one'switch to seize said last trunk when said one switch selects said last trunk at a time said last trunk is in a free position, the operation of said last means also disabling said relay.

In a telephone system, a station having a dial, a switch, two groups of trunks, means for causing said switch to select and seize a free trunk in one of said groups when a single digit code is dialed at said station, means for causing said switch to select the first trunk of said other group when a two digit code is dialed at said station, means for automatically causing said switch to by-pass the first and intermediate trunks of said other group when said first and intermediate trunks are busy at a time said switch selects said first trunk, relay means responsive to the selection of the last trunk of said other group by said switch for stopping said switch on said last trunk, and means responsive to said stopping of said switch for causing said switch to seize said last trunk.

i. In a telephone system, a group of switches, a group of trunks accessible to said switches, means for causing any one of said switches to select the last trunk of said trunk group, a relay partially operated responsive to the selection of said last trunk by one of said switches, means responsive to said partial operation of said relay for fully operating said relay when said one switch selects said last trunk at a time said last trunk is in a busy condition, means responsive to said full operation of said relay for preventing further selective action of said one switch, and means also responsive to said full operation of said relay for causing busy tone to be applied to said switch.

5. In a telephone system, a group of switches, a group of trunks accessible to said switches, means for causing one of said switches to select the last trunk of said trunk group, a relay operated responsive to said selection of said last trunk for stopping said switch on said selected last trunk, means for locking said operated relay when said stopping of said switch occurs at a time said last trunk is in a busy condition, and means including contacts of said locked relay for preventing further selective action of said one switch and for completing a busy tone circuit.

6. In a telephone system, a station having a dial, a switch, two groups of trunks, means for causing said switch to select a free trunk in one of said groups when a single digit code is dialed at said station, means for causing said switch to select the first trunk of said other group when a two digit code is dialed at said station, means for causing said switch to pass over the first and intermediate trunks of said other group when said first and intermediate trunks of said other group are busy at a time said switch selects said first trunk, a first relay partially oper ted es n ve to th selec on o i t e o tl un of i1 the 510 11 a s nd relay ar al p at esp mir to ol fil Qil o said last trunk oi said other groups, means responsiye to said partial operation of either of said two relays for stopping said switch on said last trunk of said other groups, means responsive to said partial operation of said first relay for fully'ope'rating said first relay, means controlled bysaid full operation of said first relay for hold- 111g said stop switch on said last trunl; oi said other group, and means controlled bywsaid fu1l operation of said first relay for causing the restoration of ai p t a l op r -le secon a relay.

7. In a telephone system, a group of switches, a group of trunk? accessible to said switches, means for causing one of said switches to select the last trunk of said group, a relay partially operated in response to said selection of said last trunkof said'group irrespective of Whether said selection is made t the time said selected trunk is ina busy condition or in a free condition, means controlled by said partially operated relay for holding said one switch on said selected trunk, means responsive to said partial operation of said relay occurring at a time said'selected trunk is in a'busy'condition for fully operating said relay, said holding means controlled by 'said operated relay for further holding said one switch on said selected trunk, means responsive to said full operation of said relay for causing busy tone to be applied to said one switch, a second relay op ra in respo s to aid el ct o o sold s t u k of. s d s oo occurrin ime said selected unk is n a tr condit n, means. 111-. dependent of said one partially operated relay and c n o e by a e a on o said econd relay for holding said one switch on said selected ru and me n ontr l e by sai per t o i e n r ay for a s sa d o part al pera d. r ay t fostot h r by t p ent an ppl a on of us t e t sa d ne i ch.

8- In a le hon s em, a switc a roup o un s oo ss lo to sold switch, m an fo cau nssolol swi h to sel ct t e l st trun oi o group a o. t me said last trun s a re ooo ditl n. two re a s. ope ated e ponsive. to olo o ooll of said a t tru mean ontr le by said operations of Solid, relay for stop in sa d wi on said el cted trunk, mea contro yv one o s lo operat r la s indepen nt of said other operated'relay ior holding said stopped swi h n d o ot d unk. a m ans o trolled by said-one operated relay for causing aid th r ope ed rel y t r s o e- HAB VEY AL JER.

FERENC S ITED,

The following references are of record in the i-lle of this patent:

UNITED STATES PATENTS 

